Instrumentation of the Root Canal System

Question 2

why is instrumentation used in the root canals

Answer 2

removed infected soft and hard tissue, give disinfecting irrigant access to apical canal space, create space for the delivery of medicaments and subsequent obutarion, raise integrity of radicular structures

get all stuff out, widen to allow bleach, make easier to kill, keep in same shape as before

Question 3

design objectives of instrumentation of RC system

Answer 3

• create a continuously tapering funnel shape
• maintain apical foramen in orginal position
• keep apical opening as small as possible

Question 4

chemo vs mechanical preparation

Answer 4

chemo = kill organisms, remove smear layer
mechanical = prepare shape, flush out

Question 5

what is the aim of chemomechanical preparation

Answer 5

shape canal, allow delivery of NaOCl to working length and create shape to obturate

Question 6

what are the challenges of root canal preparation

Answer 6

complex, number length curvature and diameter of root canals varies considerably

Question 7

estimated working length

Answer 7

estimated length at which instrumentation should be limited.
obtained by measuring pre-op radiographs to determine distance between coronal reference point and radiographic apex then subtracting 1mm

Question 8

corrected working length

Answer 8

length at which instrumentation and subsequent obutration should be limited

obtained by electronic apex locator and/or working length radiograph

Question 9

master apical file

Answer 9

largest diameter file taken to working length and therefore represents final prepared size of apical portion of canal at WL

Question 10

types of motions used in mechanical preparation

Answer 10

• filing
• reaming
• watch winding
• balanced force motion
• envelope of motion

Question 11

watch winding technique

Answer 11

back and forward oscillation of 30-60*
light apical pressure, effective with K files, useful for passing small files through canals

Question 12

barbed broach instrument

Answer 12

for extirpation not enlarging
tapered round shaft, not engage canal walls

Question 13

stainless steel instruments

Answer 13

16mm cuttig flutes
hedstrom file, reamer, k-file

Question 14

hedstrom file

Answer 14

filing motion, cuts on withdrawl
good cutting efficiency
iatrogenic damage so no longer used for canal preparation
useful for removing gutta percha or fractured instruments in retreatment

Question 15

reamer

Answer 15

twisting tapered triangle shaft
cutting edges parallel to cutting edge
contact with walls for effectiveness
if it binds, it breaks

Question 16

k-files

Answer 16

cutting edge perpendicular to long axis
filing motion, withdrawn while applying lateral pressure, repeat until canal enlarged

Question 17

nickel titanium instruments

Answer 17

super elasticity, can be strained more than other alloys before permanent deformation
curved canals for less lateral force exerted
less transportation, zipping, ledging
more centrally placed preparation in harmony with original canal shape

Question 18

what are the components of endodontic rotary instruments

Answer 18

• taper
• flute
• leading/cutting edge
• land
• relief
• helix angle

Question 19

taper and flute component definitions

Answer 19

taper = diameter change along working surface
flute = groove to collect dentine and soft tissue

Question 20

leading/cutting edge and land component definitions

Answer 20

leading/cutting edge = forms and deflects dentine chips
land = surface extending between flutes

Question 21

relief and helix angle component defintions

Answer 21

relief = reduction in surface of land
helix angle = angle cutting axis forms with long axis of file

Question 22

advantages of NiTi vs SS

Answer 22

increased flexibility in larger sizes and tapers, increased cutting efficiency
good safety if used appropriately, can be more user-friendly with fewer instruments and simple sequences

Question 23

disadvantages of NiTi

Answer 23

instrument fracture, expense, access difficult in posterior teeth, unsuitable for complex canal anatomy

Question 24

what is true reciprocation
adv and disadv

Answer 24

mimic of manual movement
reduces risks associated with continuously rotating a file through canal curvatures

decreased cutting efficiency, increased inward pressure required, limited capacity to auger debris out of canal

Question 25

how do you create a glide path

Answer 25

confirm straight line access, explore anaotmy, introduce 10-25 files to resistance, coronal flare, size 10 watch winding to establish apex, irrigate and repeat using size 15-20

Question 26

what is torsional stress

Answer 26

extensive instrument surface encounters excessive friction on canal walls, instrument tip is larger than canal section to be shaped, tip may lock and torque exceeds critical level

Question 27

what is flexural stress

Answer 27

repeated cyclic metal fatigue, cannot be influenced by clinician

Question 28

what is cyclic fatigue

Answer 28

freely rotating in curvature, generation of tension/compression